This invention relates to a hydraulic drive system for a civil engineering or construction machine such as a hydraulic excavator, which is suitable for arrangement in the civil engineering or construction machine and has a first control valve group connected to a first hydraulic pump and including plural directional control valves and a second control valve group connected to a second hydraulic pump and including plural directional control valves.
As conventional art of this type, there is, for example, one disclosed in JP 2642972 B2. This conventional art relates to a hydraulic circuit for a civil engineering or construction machine, and is provided with a first hydraulic pump and a second hydraulic pump.
Connected to the first hydraulic pump is a first control valve group, which is provided on a most downstream side with a bypass on/off valve having an open position and a closed position for selectively maintaining a bypass passage in or out of communication and makes up a single housing including a revolving-controlling directional control valve, an arm-controlling directional control valve, and a travel-controlling directional control valve for one of traveling motors. The individual directional control valves in this first control valve group are connected parallel to the first hydraulic pump.
Connected to the second hydraulic pump is a second control valve group, which makes up another housing including, in addition to a reserve directional control valve as an attachment-controlling directional control valve for controlling an attachment actuator for driving an attachment such as a hydraulic breaker or a hydraulic venchure, a boom-controlling directional control valve, a bucket-controlling directional control valve, and a travel-controlling directional control valve for the other traveling motor. The individual directional control valves in this second control valve group, except for the reserve directional control valve, are connected parallel to the second hydraulic pump.
Further, a communication line is arranged to communicate a delivery line from the first hydraulic pump and a supply line to the reserve directional control valve with each other. This communication line is connected at one end thereof to the housing of the first control valve group and at an opposite end thereof to the housing of the second control valve group. In other words, the communication line is arranged as an external piping outside the respective housings.
In addition, a shuttle valve is also arranged. The shuttle valve detects a pilot pressure which serves to change over the reserve directional control valve, and the shuttle valve takes it out as a control pressure for changing over the above-mentioned bypass on/off valve to the closed position.
When the reserve directional control valve is changed over in the conventional art constructed as described above, its operating pressure is applied as a control pressure to a drive portion of the bypass on/off valve in the first control valve group via the shuttle valve, and the bypass on/off valve is changed over to the closed position. Pressure oil from the first hydraulic pump is, therefore, supplied to the communication line arranged outside the two housings. This pressure oil is supplied further to the reserve directional control valve, and then to the attachment actuator controlled by the reserve directional control valve. Accordingly, the attachment actuator controlled by the reserve directional control valve is driven by the pressure oil from the first hydraulic pump rather than pressure oil from the second hydraulic pump connected to the second control valve group to which the reserve directional control valve belongs.
In the above-mentioned conventional art, the communication line through which the pressure oil from the first hydraulic pump is guided to the reserve directional control valve is a line arranged outside the housings in which the first control valve group and the second control valve group are accommodated, respectively, in other words, is an external line. The communication line, therefore, tends to become longer, leading to problems that a pressure loss tends to become large and the accuracy of control of attachment actuators tends to drop.
Further, the above-mentioned communication line is connected at the one end thereof to the housing in which the first control valve group is accommodated and at the opposite end thereof to the housing in which the second control valve group is accommodated. Oil leakage, therefore, tends to occur at both of the connected parts. Occurrence of such oil leakage leads to insufficiency in the amount of oil in the circuit and also to contamination of surrounding equipment with the oil.
Additional work is required to connect the one end of the communication line to the housing in which the first control valve group is accommodated and also to connect the opposite end of the communication line to the housing in which the second control valve group is accommodated. Accordingly, assembly work of the hydraulic circuit, that is, the hydraulic drive system becomes irksome, thereby leading to a reduction in the efficiency of the assembly work.
In the above-mentioned conventional art, it is only the pressure oil delivered from the first hydraulic pump that is supplied to the reserve directional control valve. The operating speed of the attachment actuator controlled by the reserve directional control valve is, therefore, limited in a wholesale manner to a slow speed (the first speed). It is, therefore, impossible to change the maximum value of the operating speed of the attachment actuator, for example, to set the operating speed of the attachment actuator at two speeds consisting of a slow speed and a fast speed. This has led to a problem that no improvement can be expected in the efficiency of work to be performed by the operation of the attachment actuator.
The present invention has been completed in view of the above-described circumstances of the conventional art, and a first object of the present invention is to provide a hydraulic drive system for a civil engineering or construction machine, which can shorten the length of a communication line through which a hydraulic pump, which is arranged to supply pressure oil to a control valve group in which no reserve directional control valve is included, and a reserve directional control valve are connected with each other, can prevent oil leakage from the communication line, can obviate connection work for the communication line, and can change the maximum value of the operating speed of the actuator controlled by the reserve directional control valve.
A second object of the present invention is to provide a hydraulic drive system for civil engineering or construction machine, which can change the maximum value of the operating speed of an actuator controlled by a reserve directional control valve and can also achieve good combined operation of the actuator, which is controlled by the reserve directional control valve, and an actuator which is controlled by a specific directional control valve belonging to a control valve group without the reserve directional control valve and may be applied with a load pressure higher than a load pressure too the actuator controlled by the reserve directional control valve.
To achieve the above-described first object, the present invention provides in a first aspect thereof a hydraulic drive system for a civil engineering or construction machine, said system being provided with a first hydraulic pump and a second hydraulic pump, a first control valve group connected to the first hydraulic pump, provided on a most downstream side thereof with a bypass on/off valve having an open position and a closed position for selectively maintaining a bypass passage in or out of communication, and a second control valve group connected to the second hydraulic pump and comprised of plural directional control valves including a reserve directional control valve, characterized in that the system is provided with a communication line communicating a most upstream side of the first control valve group with a supply line to the reserve directional control valve, a merge control valve having an open position and a closed position to selectively maintain the communication line in or out of communication, an interlocked control means for permitting an operation to change over the merge control valve to the open position and the bypass on/off valve to the closed position in association with a change-over operation of a reserve control device for changing over the reserve directional control valve, and a selective change-over means capable of selectively taking one of a state, in which the operation to change over the merge control valve to the open position by the interlocked control means is feasible, and another state in which the operation to change over the merge control valve to the open position by the interlocked control means is infeasible; and the first control valve group, the second control valve group, the communication line and the merge control valve are arranged in a single housing.
In the first aspect constructed as described above, the reserve directional control valve is changed over from a neutral position when the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective change-over means has been operated to inhibit a change-over operation of the merge control valve to the closed position by the interlocked control means. At this time, the merge control valve is maintained in the closed position by the selective change-over means as mentioned above. Accordingly, the pressure oil from the first hydraulic pump cannot be supplied to the supply line to the reserve directional control valve via the merge control valve and the communication line, and only the pressure oil from the second hydraulic pump is supplied to the reserve directional control valve. Described specifically, only the pressure oil from the second hydraulic pump is supplied to the actuator controlled by the reserve directional control valve to operate the actuator at a relatively slow speed.
When a directional control valve belonging, for example, to the first control valve group connected to the first hydraulic pump is changed over in this state, the pressure oil from the first hydraulic pump is supplied via the directional control valve to its corresponding actuator, thereby making it possible to achieve a combined operation of the corresponding actuator and the actuator controlled by the reserve directional control valve.
When the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective change-over means has been operated to permit a change-over operation of the merge control valve to its open position by the interlocked control means, the reserve directional control valve is changed over from the neutral position. Concurrently with this, the interlocked control means is operated to change over the merge control valve to the open position and the bypass on/off valve to the closed position, respectively. As a consequence, the pressure oil from the first hydraulic pump is guided to the supply line to the reserve directional control valve via the merge control valve and the communication line. In other words, the pressure oil from the first hydraulic pump and the pressure oil from the second hydraulic pump are both supplied to the reserve directional control valve and further to the actuator controlled by the reserve directional control valve. Therefore, the actuator controlled by the reserve directional control valve can be operated at a fast speed faster than the above-mentioned operating speed.
As has been described above, the maximum value of the operating speed of the actuator controlled by the reserve directional control valve can be selectively changed by an operation of the selective change-over means to the slow speed available by the supply of the pressure oil only from the second hydraulic pump or the fast speed available by the merging of the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump.
Further, the communication line through which the most upstream side of the first control valve group and the supply line to the reserve directional control valve are communicated with each other, and the merge control valve are arranged within the same single housing as the first control valve group in which the reserve directional control valve is not included and the second control valve group in which the reserve directional control valve is included. In particular, the communication line is not an external line so that the communication line is not arranged surrounding the housing. Accordingly, the length of the communication line can be set extremely short.
The communication line is arranged within the housing, and a connection part at the most upstream side of the first control valve group, to which connection part the communication line is connected at the one end thereof, and a connection part of the supply line to the reserve directional control valve, to which connection part the communication line is connected at the opposite end thereof, are both located within the housing. It is, therefor, possible to prevent leakage of oil supplied to the communication line, in other words, leakage of oil from the housing.
Moreover, the connection part at the most upstream side of the first control valve group, to which connection part the communication line is connected at the one end thereof, and the connection part of the supply line to the reserve directional control valve, to which connection part the communication line is connected at the opposite end thereof, can be both formed upon fabrication of the housing. No additional line connecting work is therefore needed for the communication line.
To achieve the first object, the present invention also provides in a second aspect thereof a hydraulic drive system as described above in connection with the first aspect, wherein the reserve directional control valve comprises a hydraulically-operated pilot valve, the reserve control device comprises a pilot-operated control device for outputting a pilot pressure to change over the reserve directional control valve, and the merge control valve and the bypass on/off valve comprise hydraulically-operated pilot valves, respectively, the interlocked control means includes a shuttle valve, which can detect apilot pressure outputted from the reserve control device and can output the pilot pressure as a pressure signal for changing over the merge control valve to the open position and the bypass on/off valve to the closed position, and a pilot line communicating the shuttle valve with respective drive portions of the merge control valve and the bypass on/off valve, and the selective change-over means includes a selective control valve arranged in a part of the pilot line, which communicates the shuttle valve with the drive portion of the merge control valve, and capable of selectively taking one of a first state in which a pilot pressure outputted from the shuttle valve can be supplied to the drive portion of the merge control valve and a second state in which a pilot pressure outputted from the shuttle valve cannot be supplied to the drive portion of the merge control valve.
In the second aspect constructed as described above, the reserve directional control valve is changed over from the neutral position by a pilot pressure outputted from a reserve control device when the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective control valve has been changed over to inhibit a change-over operation of the merge control valve to the open position by the pilot pressure outputted from the reserve control device. At this time, the merge control valve is maintained in the closed position by the selective control valve as mentioned above. Accordingly, the pressure oil from the first hydraulic pump cannot be supplied to the supply line to the reserve directional control valve via the merge control valve and the communication line, and only the pressure oil from the second hydraulic pump is supplied to the reserve directional control valve. Described specifically, only the pressure oil from the second hydraulic pump is supplied to the actuator controlled by the reserve directional control valve to operate the actuator at a relatively slow speed.
When a directional control valve belonging, for example, to the first control valve group connected to the first hydraulic pump is changed over in this state, the pressure oil from the first hydraulic pump is supplied via the directional control valve to its corresponding actuator, thereby making it possible to achieve a combined operation of the corresponding actuator and the actuator controlled by the reserve directional control valve.
When the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective control valve has been changed over to permit a change-over operation of the merge control valve to its open position by a pilot pressure outputted from the reserve control device, the reserve directional control valve is changed over from the neutral position by the pilot pressure outputted from the reserve control device. Concurrently with this, the pilot pressure outputted from the reserve control device is applied to the drive portion of the merge control valve and the drive portion of the bypass on/off valve, respectively, via the shuttle valve, the selective control valve and the pilot line, and the merge control valve and the bypass on/off valve are changed over to the open position and the closed position, respectively. As a consequence, the pressure oil from the first hydraulic pump is guided to the supply line to the reserve directional control valve via the merge control valve and the communication line. In other words, the pressure oil from the first hydraulic pump and the pressure oil from the second hydraulic pump are both supplied to the reserve directional control valve and further to the actuator controlled by the reserve directional control valve. Therefore, the actuator controlled by the reserve directional control valve can be operated at a fast speed faster than the above-mentioned operating speed.
As has been described above, the maximum value of the operating speed of the actuator controlled by the reserve directional control valve can be selectively changed by an operation of the selective change-over means to the slow speed available by the supply of the pressure oil only from the second hydraulic pump or the fast speed available by the merging of the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump.
To achieve the first object, the present invention also provides in a third aspect thereof a hydraulic drive system as described above in connection with the second aspect, wherein the selective control valve comprises a solenoid valve and the selective change-over means includes a selector switch for outputting an electrical signal to selectively actuate the selective control valve such that the selective control valve is maintained in one of the first state and the second state.
In the third aspect constructed as described above, the selective control valve can be maintained, depending upon an operation of the selector switch, in either the first state in which a change-over operation of the merge control valve to the open position by a pilot pressure outputted from the reserve control device is feasible or the second state in which a change-over operation of the merge control valve to the open position by a pilot pressure outputted from the reserve control device is infeasible.
To achieve the first object, the present invention also provides in a fourth aspect thereof a hydraulic drive system as described above in connection with the first aspect, wherein the selective change-over means and the bypass on/off valve comprise hydraulically-operated pilot valves, respectively, the interlocked control means includes a predetermined hydraulic pressure source and a pilot line for guiding a pilot pressure, which has been outputted from the predetermined hydraulic pressure source, as a pressure signal to change over the merge control valve to the open position and at the same time, as a pressure signal to change over the bypass on/off valve to the closed position, and the selective change-over means includes a selective control valve arranged in a part of the pilot line, which communicates the predetermined hydraulic pressure source with the drive portion of the merge control valve, and capable of selectively taking one of a first state in which a pilot pressure outputted from the predetermined hydraulic pressure source can be supplied to the drive portion of the merge control valve and a second state in which a pilot pressure outputted from the predetermined hydraulic pressure source cannot be supplied to the drive portion of the merge control valve, and an operation detecting means for detecting an operation of the reserve control device to output an electrical signal such that the selective control valve is selectively operated to remain in one of the first state and the second state.
In the fourth aspect constructed as described above, an operation of the reserve control device to operate the actuator controlled by the reserve directional control valve can change over the reserve directional control valve from the neutral position provided that the selective control valve is set to inhibit a change-over operation of the merge control valve to the open position by a pilot pressure outputted from the predetermined hydraulic pressure source, for example, when the operation detecting means detects an operation of the reserve control device. At this time, the merge control valve is maintained in the closed position by the selective control valve as mentioned above. Accordingly, the pressure oil from the first hydraulic pump cannot be supplied to the supply line to the reserve directional control valve via the merge control valve and the communication line, and only the pressure oil from the second hydraulic pump is supplied to the reserve directional control valve. Described specifically, only the pressure oil from the second hydraulic pump is supplied to the actuator controlled by the reserve directional control valve to operate the actuator at a relatively slow speed.
When a directional control valve belonging, for example, to the first control valve group connected to the first hydraulic pump is changed over in this state, the pressure oil from the first hydraulic pump is supplied via the directional control valve to its corresponding actuator, thereby making it possible to achieve a combined operation of the corresponding actuator and the actuator controlled by the reserve directional control valve.
Provided that the selective control valve has been set to permit a change-over operation of the merge control valve to the open position by a pilot pressure outputted from the predetermined hydraulic pressure source, for example, when the operation detecting means detects an operation of the reserve control device, an operation of the reserve control device to operate the actuator controlled by the reserve directional control valve results in a change-over of the reserve directional control valve from the neutral position. Concurrently with this, the operation of the reserve control device is detected by the operation detecting means, a pilot pressure outputted from predetermined hydraulic source is applied to the drive portion of the merge control valve and the drive portion of the bypass on/off valve, respectively, via the selective control valve and the pilot line, and the merge control valve and the bypass on/off valve are changed over to the open position and the closed position, respectively. As a consequence, the pressure oil from the first hydraulic pump is guided to the supply line to the reserve directional control valve via the merge control valve and the communication line. In other words, the pressure oil from the first hydraulic pump and the pressure oil from the second hydraulic pump are both supplied to the reserve directional control valve and further to the actuator controlled by the reserve directional control valve. Therefore, the actuator controlled by the reserve directional control valve can be operated at a fast speed faster than the above-mentioned operating speed.
As has been described above, the maximum value of the operating speed of the actuator controlled by the reserve directional control valve can be selectively changed to the slow speed available by the supply of the pressure oil only from the second hydraulic pump or the fast speed available by the merging of the pressure oil from the first hydraulic pump with the pressure oil from the second hydraulic pump.
To achieve the first object, the present invention also provides in a fifth aspect thereof a hydraulic drive system as described above in connection with the first aspect, wherein the hydraulic drive system further comprises a merge control valve control means for controlling the merge control valve such that the merge control valve is changed over to the closed position in response to an operation of a desired directional control valve included in the first control valve group.
In the fifth aspect constructed as described above, when a predetermined directional control valve in the first control valve group in which the reserve directional control valve is not included is operated, for example, in a state that the selective change-over means has been operated and changed over into a state where a change-over operation of the merge control valve to the open position by the interlocked control means is feasible, the reserve control device has been operated and the reserve directional control valve has been changed over and the actuator controlled by the reserve directional control valve is operating at a fast speed by the pressure oil supplied and merged from the first hydraulic pump and the second hydraulic pump, the merge control valve control means is operated to change over the merge control valve from the open position to the closed position. As a consequence, the pressure oil from the first hydraulic pressure is blocked by the merge control valve and is no longer supplied to the reserve directional control valve. Namely, the pressure oil from the first hydraulic pump is supplied to the predetermined directional control valve, and only the pressure oil from the second hydraulic pump is supplied to the reserve directional control valve. Therefore, the actuator controlled by the predetermined directional control valve operates at a speed commensurate with a flow rate at which the pressure oil is supplied from the first hydraulic pump, while the actuator controlled by the reserve directional control valve changes to a slow speed commensurate with a flow rate at which the pressure oil is supplied from the second hydraulic pump.
As has been described above, it is possible to perform a combined operation of the actuator controlled by the reserve directional control valve and the actuator controlled by the predetermined directional control valve, although the operating speed of the actuator controlled by the reserve directional control valve changes from a fast sped to a slow speed.
To achieve the first object, the present invention also provides in a sixth aspect thereof a hydraulic drive system as described above in connection with the first aspect, wherein the predetermined directional control valve comprises a hydraulically-operated pilot valve, a predetermined directional control valve control device for changing over the predetermined directional control valve comprises a pilot control device for outputting a pilot pressure, the reserve directional control valve comprises a hydraulically-operated pilot valve, the reserve control device comprises a pilot control device for outputting a pilot pressure to change over the reserve directional control valve, and the merge control valve and the bypass on/off valve comprises hydraulically-operated pilot valves, respectively, the interlocked control means includes a first shuttle valve, which can detect a pilot pressure outputted from the reserve control device and can output the pilot pressure as a pressure signal for changing over the merge control valve to the open position and the bypass on/off valve to the closed position, and a first pilot line communicating the first shuttle valve with respective drive portions of the merge control valve and the bypass on/off valve, the selective change-over means includes a selective control valve arranged in a part of the first pilot line, which communicates the first shuttle valve with the drive portion of the merge control valve, and capable of selectively taking one of a first state in which a pilot pressure outputted from the first shuttle valve can be supplied to the drive portion of the merge control valve and a second state in which a pilot pressure outputted from the first shuttle valve cannot be supplied to the drive portion of the merge control valve, and the merge control valve control means includes a second shuttle valve, which can detect a pilot pressure outputted from the predetermined directional control valve control device and can output the pilot pressure as a pressure signal for changing over the merge control valve, and a second pilot line communicating the second shuttle valve with a drive portion of the merge control valve.
In the sixth aspect constructed as described above, the reserve directional control valve is changed over from the neutral position by a pilot pressure outputted from a reserve control device when the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective control valve has been changed over to inhibit a change-over operation of the merge control valve to the open position by the pilot pressure outputted from the reserve control device. At this time, the merge control valve is maintained in the closed position by the selective control valve as mentioned above. Accordingly, the pressure oil from the first hydraulic pump cannot be supplied to the supply line to the reserve directional control valve via the merge control valve and the communication line, and only the pressure oil from the second hydraulic pump is supplied to the reserve directional control valve. Described specifically, only the pressure oil from the second hydraulic pump is supplied to the actuator controlled by the reserve directional control valve to operate the actuator at a relatively slow speed.
When a directional control valve belonging, for example, to the first control valve group connected to the first hydraulic pump is changed over in this state, the pressure oil from the first hydraulic pump is supplied via the directional control valve to its corresponding actuator, thereby making it possible to achieve a combined operation of the corresponding actuator and the actuator controlled by the reserve directional control valve.
When the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective control valve has been changed over to permit a change-over operation of the merge control valve to its open position by a pilot pressure outputted from the reserve control device, the reserve directional control valve is changed over from the neutral position by the pilot pressure outputted from the reserve control device. Concurrently with this, the pilot pressure outputted from the reserve control device is applied to the drive portion of the merge control valve and the drive portion of the bypass on/off valve, respectively, via the first shuttle valve, the selective control valve and the first pilot line, and the merge control valve and the bypass on/off valve are changed over to the open position and the closed position, respectively. As a consequence, the pressure oil from the first hydraulic pump is guided to the supply line to the reserve directional control valve via the merge control valve and the communication line. In other words, the pressure oil from the first hydraulic pump and the pressure oil from the second hydraulic pump are both supplied to the reserve directional control valve and further to the actuator controlled by the reserve directional control valve. Therefore, the actuator controlled by the reserve directional control valve can be operated at a fast speed faster than the above-mentioned operating speed.
When the predetermined directional control valve control device is operated, for example, in a state that the pressure oil from the first hydraulic pump and the pressure oil from the second hydraulic pump are both supplied to the reserve directional control valve, the predetermined directional control valve belonging to the first control valve group in which the reserve directional control valve is not included is changed over from the neutral position by a pilot pressure outputted from the predetermined directional control valve control device. Concurrently with this, a pilot pressure outputted from the predetermined directional control valve control device is detected by the second shuttle valve and is applied to the drive portion of the merge control valve via the second pilot line. The merge control valve is, therefore, changed over from the open position to the closed position. As a consequence, the pressure oil from the first hydraulic pressure is blocked by the merge control valve and is no longer supplied to the reserve directional control valve. Namely, the pressure oil from the first hydraulic pump is supplied to the predetermined directional control valve, and only the pressure oil from the second hydraulic pump is supplied to the reserve directional control valve.
As has been described above, when the predetermined directional control valve is operated, the actuator controlled by the predetermined directional control valve can be operated by the pressure oil from the first hydraulic pump, and the maximum value of the operating speed of the actuator controlled by the reserve directional control valve is set at the slow speed which depends solely upon the pressure oil from the second hydraulic pump.
To achieve the first object, the present invention also provides in a seventh aspect thereof a hydraulic drive system as described above in connection with the sixth aspect, wherein the first shuttle valve and the second shuttle valve are accommodated within a shuttle block composed of a single housing.
According to the seventh aspect constructed as described above, a group of shuttle valves can be arranged together.
To achieve the second object, on the other hand, the present invention also provides in an eighth aspect thereof a hydraulic drive system for a civil engineering or construction machine, said system being provided with a first hydraulic pump and a second hydraulic pump, a first control valve group connected to the first hydraulic pump, provided on a most downstream side thereof with a bypass on/off valve having an open position and a closed position for selectively maintaining a bypass passage in or out of communication, and a second control valve group connected to the second hydraulic pump and comprised of plural directional control valves including a reserve directional control valve, characterized in that the system is provided with a communication line communicating a most upstream side of the first control valve group with a supply line to the reserve directional control valve, a merge control valve having an open position and a closed position to selectively maintain the communication line in or out of communication, an interlocked control means for permitting an operation to change over the merge control valve to the open position and the bypass on/off valve to the closed position in association with a change-over operation of a reserve control device for changing over the reserve directional control valve, a selective change-over means capable of selectively taking one of a state, in which the operation to change over the merge control valve to the open position by the interlocked control means is feasible, and another state in which the operation to change over the merge control valve to the open position by the interlocked control means is infeasible, and a valve opening area control means for controlling drive of the merge control valve such that, when a specific directional control valve included in the first control valve group for controlling drive of an actuator to which a load pressure higher than a load pressure to an actuator controlled by the reserve directional control valve may be applied is operated concurrently with a change-over operation of the reserve directional control valve by the reserve control device, a valve opening area of the merge control valve is changed to a predetermined small valve opening area.
In the eighth aspect constructed as described above, the reserve directional control valve is changed over from a neutral position when the reserve control device is operated to operate the actuator controlled by the reserve directional control valve, for example, in a state that the selective change-over means has been operated to permit a change-over operation of the merge control valve to the open position by the interlocked control means. Concurrently with this, the interlocked control means is operated to change over the merge control valve and the bypass on/off valve to the open position and the closed position, respectively. Accordingly, the pressure oil from the first hydraulic pump is guided to the supply line to the reserve directional control valve via the merge control valve and the communication line. Namely, the pressure oil from the first hydraulic pump and the pressure oil from the second hydraulic pump are both supplied to the reserve directional control valve and further to the actuator controlled by the reserve directional control valve. The actuator controlled by the reserve directional control valve can be operated at a fast speed accordingly.
When, as mentioned above, the specific directional control valve included in the first control valve group is operated and changed over either after the reserve control device has been operated and the reserve directional control valve has been changed over from the neutral position or concurrently with a change-over operation of the reserve directional control valve from the neutral position in a state that the selective change-over means has been operated to permit a change-over operation of the merge control valve to the open position by the interlocked control means, the valve opening area control means operates such that the valve opening area of the merge control valve is controlled to the predetermined small valve open area.
As a result, the merge control valve is controlled such that the supply of the pressure oil from the first hydraulic pump to the reserve directional control valve via the merge control valve is reduced, and therefore, a sufficient portion of the pressure oil from the first hydraulic pump can be supplied to the specific directional control valve. Accordingly, the actuator controlled by the specific directional control valve, in other words, the actuator to which a load pressure higher than that to be applied to the actuator controlled by the reserve directional control valve may be applied can be driven together with the actuator controlled by the reserve directional control valve, thereby making it possible to achieve a good combined operation of these actuators.
To achieve the second object, the present invention also provides in a ninth aspect thereof a hydraulic drive system as described above in connection with the eighth aspect, wherein the reserve directional control valve comprises a hydraulically-operated pilot valve, the reserve control device comprises a pilot-operated control device for outputting a pilot pressure to change over the reserve directional control valve, and the merge control valve and the bypass on/off valve comprise hydraulically-operated pilot valves, respectively, the interlocked control means includes a shuttle valve, which can detect a pilot pressure outputted from the reserve control device and can output the pilot pressure as a pressure signal for changing over the merge control valve to the open position and the bypass on/off valve to the closed position, and a pilot line communicating the shuttle valve with respective drive portions of the merge control valve and the bypass on/off valve, and the selective change-over means includes a selective control valve arranged in a part of the pilot line, which communicates the shuttle valve with the drive portion of the merge control valve, and capable of selectively taking one of a first state in which a pilot pressure outputted from the shuttle valve can be supplied to the drive portion of the merge control valve and a second state in which a pilot pressure outputted from the shuttle valve cannot be supplied to the drive portion of the merge control valve.
To achieve the second object, the present invention also provides in a tenth aspect thereof a hydraulic drive system as described above in connection with the ninth aspect, wherein the selective control valve comprises a solenoid valve; and the valve opening area control means includes a specific operation detecting means for detecting an operation of the specific directional control valve, which is included in the first control valve group, and outputting an electrical signal, and a controller for performing a predetermined computation based on the electrical signal outputted from the specific operation detecting means and outputting a control signal, which is commensurate with results of the computation, as a signal for driving the selective control valve.
In the tenth aspect constructed as described above, when an operation of the specific directional control valve included in the first control valve group is detected by the specific operation detecting means, an electrical signal is outputted to the controller from the specific operation detecting means. The controller outputs a control signal, which is commensurate with the electrical signal, to the drive portion of the selective control valve, and accordingly, the shuttle valve is restricted such that a pilot pressure to be supplied from the shuttle valve to the drive portion of the merge control valve becomes lower. As a consequence, the merge control valve is controlled such that its valve opening area is reduced to a predetermined small valve opening area.